Region-specific endogenous brain rhythms and their role for speech and language

Brain rhythms at different timescales are observed ubiquitously across cortex. Despite this ubiquitousness, individual brain areas can be characterized by ‘spectral profiles’, which reflect distinct patterns of endogenous brain rhythms. Crucially, endogenous brain rhythms have often been explicitly or implicitly related to perceptual and cognitive functions. Regarding language, a vast amount of research investigates the role of brain rhythms for speech processing. Particularly, lower-level processes, such as speech segmentation and consecutive syllable encoding and the hemispheric lateralization of such processes, have been related to auditory cortex brain rhythms in the theta and gamma range and explained by neural oscillatory models. Other brain rhythms —particularly delta and beta— have been related to prosodic processing (delta) but also higher-level language processing, including phrasal and sentential processing. Delta and beta brain rhythms have also been related to predictions from the motor cortex, emphasizing the tight link between production and perception. More recently, neural oscillatory models were extended to include different levels of language processing. Attempts to directly relate these brain rhythms observed during task-related processing to endogenous brain rhythms are sparse. In summary, many questions remain: the functional relevance of brain rhythms with respect to speech and language continues to be a subject of heated discussion, and research that systematically links endogenous brain rhythms to specific computations and possible algorithmic implementations is rare.